Dataset Information

Ancestral body plan and adaptive radiation of sauropterygian marine reptiles.

ABSTRACT: Sauropterygia is the most diversified and dominant clade among marine reptiles, but their early evolution is scarcely understood. Here we report the earliest known complete specimen related to sauropterygians from the Early Triassic. It is referred to Hanosaurus hupehensis by an exclusive combination of features and shows mosaic morphology integrating the characters of multiple sauropterygian sub-lineages. In phylogenetic results from both parsimony and Bayesian analyses employing our reconstructed dataset, Hanosaurus is stably resolved as the basal-most member of Sauropterygiformes, a clade comprising all sauropterygians and saurosphargids. This skeleton reveals an unexpected ancestral body plan for sauropterygiforms with an elongate trunk and four short limbs, differing from many of its immediate descendants but more similar to non-sauropterygiform marine reptiles at their early aquatic stage as axial swimmers. After this convergence on body plan, we quantitatively confirm the rapid divergence of sauropterygiform reptiles following the end-Permian mass extinction.

SUBMITTER: Wang W

PROVIDER: S-EPMC9722468 | biostudies-literature | 2022 Dec

REPOSITORIES: biostudies-literature

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Ancestral body plan and adaptive radiation of sauropterygian marine reptiles.

Wang Wei W Shang Qinghua Q Cheng Long L Wu Xiao-Chun XC Li Chun C

iScience 20221118 12

Sauropterygia is the most diversified and dominant clade among marine reptiles, but their early evolution is scarcely understood. Here we report the earliest known complete specimen related to sauropterygians from the Early Triassic. It is referred to <i>Hanosaurus hupehensis</i> by an exclusive combination of features and shows mosaic morphology integrating the characters of multiple sauropterygian sub-lineages. In phylogenetic results from both parsimony and Bayesian analyses employing our rec ...[more]

PMID: 36483013

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Project description:BACKGROUND:Early Cambrian Lagerstätten from China have greatly enriched our perspective on the early evolution of animals, particularly arthropods. However, recent studies have shown that many of these early fossil arthropods were more derived than previously thought, casting uncertainty on the ancestral euarthropod body plan. In addition, evidence from fossilized neural tissues conflicts with external morphology, in particular regarding the homology of the frontalmost appendage. RESULTS:Here we redescribe the multisegmented megacheirans Fortiforceps and Jianfengia and describe Sklerolibyon maomima gen. et sp. nov., which we place in Jianfengiidae, fam. nov. (in Megacheira, emended). We find that jianfengiids show high morphological diversity among megacheirans, both in trunk ornamentation and head anatomy, which encompasses from 2 to 4 post-frontal appendage pairs. These taxa are also characterized by elongate podomeres likely forming seven-segmented endopods, which were misinterpreted in their original descriptions. Plesiomorphic traits also clarify their connection with more ancestral taxa. The structure and position of the "great appendages" relative to likely sensory antero-medial protrusions, as well as the presence of optic peduncles and sclerites, point to an overall homology with the anterior head of radiodontans. This is confirmed by our Bayesian phylogeny, which places jianfengiids as the basalmost euarthropods, paraphyletic with other megacheirans, and in contiguity with isoxyids and radiodontans. CONCLUSIONS:Sklerolibyon and other jianfengiids expand the disparity of megacheirans and suggest that the common euarthropod ancestor possessed a remarkable phenotypic variability associated with the externalized cephalon, as well as endopods that were already heptopodomerous, which differs from previous hypotheses and observations. These animals also demonstrate that the frontalmost pair of arthrodized appendage is homologous between radiodontans and megacheirans, refuting the claim that the radiodontan frontal appendages evolved into the euarthropod labrum, and questioning its protocerebral identity. This evidence based on external anatomy now constitutes a solid benchmark upon which we should address issues of homology, with the help of carefully examined palaeoneurological data.

Dataset Information

Ancestral body plan and adaptive radiation of sauropterygian marine reptiles.

Publications

Ancestral body plan and adaptive radiation of sauropterygian marine reptiles.

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